Such a type of self-propelled crushing machine is constructed such that a hopper, a crusher, a belt conveyor et cetera are incorporated into a base carrier. This self-propelled crushing machine operates as follows. An object (to be crushed) is dumped into the hopper and crushed by the crusher and crushed pieces of the object are conveyed from the crusher to outside the crushing machine by means of the belt conveyor.
However, there are cases where these crushed object pieces include metallic materials (magnetic materials) such as concrete reinforcing steel bar, nails and wire. To cope with the situations, there is proposed a self-propelled crushing machine which employs a magnetic separator disposed over a belt conveyor so that magnetic materials are selectively removed from the crushed object during conveyance by the belt conveyor (see JP-A-2003-159546).
Referring to FIGS. 8(a) and 8(b), there is illustrated a magnetic separator 100 which is provided with a magnetic separator belt 103 which moves in a direction orthogonal to the travel direction of a conveyor belt 102 in a belt conveyor 101. It is arranged such that a magnet 105 exerts magnetic force to a concrete reinforcing steel bar (magnetic material) 104 on the conveyor belt 102 through the magnetic separator belt 103, whereby the concrete reinforcing steel bar 104 is attracted and adhered to the magnetic separator belt 103 and taken off of the conveyor belt 102.
Incidentally, as shown in FIG. 8(a), upon attraction and adhesion of a leading end 104a of the concrete reinforcing steel bar 104 to the magnetic separator belt 103, the leading end 104a of the concrete reinforcing steel bar 104 is moved together with the magnetic separator belt 103 while on the other hand a trailing end 104b of the concrete reinforcing steel bar 104 is moved together with the conveyor belt 102.
At time point T1 (the moment at which the leading end 104a of the concrete reinforcing steel bar 104 has been attracted and adhered to the magnetic separator belt 103), the concrete reinforcing steel bar 104, when viewed from the side of the conveyor belt 102, is placed in a tilted position to form an acute angle a with the conveyor belt 102, as illustrated in FIG. 8(a).
At time point T2 (the moment at which the trailing end 104b of the concrete reinforcing steel bar 104 has reached line L indicative of a leading end attraction/adhesion position at which the leading end 104a of the concrete reinforcing steel bar 104 is to be attracted and adhered to the magnetic separator belt 103), the concrete reinforcing steel bar 104, when viewed from the side of the conveyor belt 102, is placed in an upright position that forms a right angle with the conveyor belt 102, as illustrated in FIG. 8(a′).
Therefore, conventional self-propelled crushing machines may cause the problem that the trailing end 104b of the concrete reinforcing steel bar 104 will pierce into the conveyor belt 102 if the relationship in belt velocities between the conveyor belt 102 and the magnetic separator belt 103 is such that the concrete reinforcing steel bar 104 is still on the conveyor belt 102 as shown in FIG. 8(b′) at time point T2 at which the concrete reinforcing steel bar 104 is placed in an upright position as shown in FIG. 8(a′).
The present invention is directed to overcoming the foregoing problem with the conventional technology. Accordingly, a primary object of the invention is to provide a self-propelled crushing machine capable of ensuring that, even when the object (to be crushed) contains a concrete reinforcing steel bar or other like material, it is prevented that the concrete reinforcing steel bar will pierce into the conveyor belt.